Tài liệu Formatting Column Values When Outputting Data as XML pptx

[ Team LiB ]Recipe 8.9 Formatting Column Values When Outputting Data as XML Problem You need to save some of the columns in a DataTable as attributes instead of elements when you write

[ Team LiB ]

Recipe 8.9 Formatting Column Values When Outputting Data as XML

Problem

You need to save some of the columns in a DataTable as attributes instead of elements when you write out the data as XML

Solution

Use the ColumnMapping property

The sample code contains two event handlers:

Form.Load

Sets up the sample by creating a DataSet containing the first two records of the Customers table from Northwind

Refresh Button.Click

Iterates over all of the columns in all of the Customers tables and sets the

ColumnMapping property to the specified value The ColumnMapping for the ContactName column is then set to the specified value The XML output for the DataSet is displayed

The C# code is shown in Example 8-13

Example 8-13 File: XmlElementsOrAttributesForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Data;

using System.Data.SqlClient;

private DataSet ds;

//

private void XmlElementsOrAttributesForm_Load(object sender,

System.EventArgs e)

{

ds = new DataSet("CustomersDataSet");

// Get the top two rows from the Customers table

SqlDataAdapter da = new SqlDataAdapter(

"SELECT TOP 2 * FROM Customers",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(ds, "Customers");

}

private void refreshButton_Click(object sender, System.EventArgs e)

{

// Set the mapping type for each column in the table

foreach(DataTable table in ds.Tables)

foreach(DataColumn column in table.Columns)

{

if(tableAttributeRadioButton.Checked)

column.ColumnMapping = MappingType.Attribute;

else if(tableElementRadioButton.Checked)

column.ColumnMapping = MappingType.Element;

else if(tableHiddenRadioButton.Checked)

column.ColumnMapping = MappingType.Hidden;

}

// Set the mapping type for the ContactName column

DataColumn dc = ds.Tables["Customers"].Columns["ContactName"];

if(columnAttributeRadioButton.Checked)

dc.ColumnMapping = MappingType.Attribute;

else if(columnElementRadioButton.Checked)

dc.ColumnMapping = MappingType.Element;

else if(columnHiddenRadioButton.Checked)

dc.ColumnMapping = MappingType.Hidden;

else if(columnSimpleContentRadioButton.Checked)

dc.ColumnMapping = MappingType.SimpleContent;

// Display the XML

xmlTextBox.Text = ds.GetXml( );

}

Discussion

The ColumnMapping property of the DataColumn specifies how the value of a column will be written when the DataSet is output as an XML document with the GetXml( ) method or WriteXml( ) method The property value is one of the MappingType

enumeration values described in Table 8-5

Table 8-5 MappingType enumeration Value Description

Attribute

The value is written as an XML attribute For example:

<MyRow>

<MyColumn>my column value</MyColumn>

</MyRow>

Element

The value is written as an XML element For example:

<MyRow MyColumn="my column value" />

This is the default

Hidden The value is not written in the XML output

SimpleContent

The value is written as text in the XML element for its row For example:

<MyRow>my column value</MyRow>

This value can only be used if the table has neither Element columns nor nested relations

There is no way to set the ColumnMapping property for all columns in a DataTable or

DataSet at once Each column must be set individually

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